Background: Primary genitourinary neoplasms as well as metastasis from other sites to the genitourinary tract are common. In contrast, collision tumors, characterized by coexistence of phenotypically and genotypically distinct tumors at the same site, are distinctly rare in the genitourinary tract and pose a diagnostic challenge. The goal of this study is to present a series of such cases from a single institution highlighting the unusual clinicopathologic features of these tumors.Design: Nine cases were retrospectively identified from our surgical pathology files and included internal and consultation cases (2006-2012). All tumors were identified by H&E and immunohistochemistry as distinct primary neoplasms. In select cases, the final diagnosis was substantiated by fluorescence in-situ hybridization.Results: The study included 9 patients, 8 males and 1 female ranging in age from 34-84 years (mean 66.3 years). Collision tumors composed 7 of the 8 cases with the site of the collision as follows: kidney (6), bladder (2), and pelvis (1). All but one of the collision tumors involved two malignant neoplasms.

Collision Tumor Cases

Case

Primary Tumor

Secondary Tumor

Location

Age

Sex

1

Chromophobe Renal Cell Carcinoma

Neuroendocrine/Carcinoid Tumor

Kidney

34

M

2

Clear Cell Renal Cell Carcinoma

Pulmonary Adenocarcinoma

Kidney

57

M

3

Clear Cell Renal Cell Carcinoma

Poorly Differentiated Carcinoma of Urothelial Origin

Kidney

64

M

4

Angiomyolipoma

Mammary Carcinoma

Kidney

67

F

5

Clear Cell Renal Cell Carcinoma

Chromophobe Renal Cell Carcinoma

Kidney

76

M

6

Chromophobe Renal Cell Carcinoma

Papillary Renal Cell Carcinoma

Kidney

81

M

7

Pleomorphic Liposarcoma

Prostatic Adenocarcinoma

Pelvis

70

M

8

Urothelial Carcinoma

Prostatic Adenocarcinoma

Bladder

73

M

9

Urothelial Carcinoma

Prostatic Adenocarcinoma

Bladder

84

M

Conclusions: To our knowledge, this is the largest report of collision neoplasms of genitourinary origin. Diagnosis of collision tumors in the genitourinary tract is a perplexing task and awareness about these rare entities, thorough sampling of the tumor mass and appropriate use of ancillary techniques are recommendations for avoiding incorrect diagnosis, and pathologic staging.Category: Genitourinary (including renal tumors)